Field of the Invention
The present invention relates to a readily adhesive sheet, a protective sheet for a solar cell, a back sheet member for a solar cell, a back sheet for a solar cell and a solar cell module.
Background Art
In general, a solar cell module in which crystalline silicon, amorphous silicon or the like is used for solar cell elements is manufactured using a lamination method or the like in which a transparent front substrate on a side on which solar light enters, a cell-side substrate in which a solar cell element as a photovoltaic element is sealed with a sealing material, a rear surface protective sheet layer (back sheet for the solar cell) and the like are sequentially stacked, sucked in a vacuum, and hot-pressed. Since a solar cell is placed in an environment exposed to direct sun light and rain, such as on the roof, for a long period of time, the respective layers that configure a solar cell module are required to have a variety of functions typically including durability in a hot and humid environment.
In the past, glass was frequently used for the transparent front substrate or the back sheet for a solar cell; however, in recent years, there has been a demand for use of a protective sheet for a solar cell in which a base material mainly including a resin film is used for the front substrate or the back sheet for a solar cell since a variety of functions can be added by stacking functional layers and the cost can be reduced by decreasing the weight of the solar cell module.
The above protective sheets for a solar cell frequently form a laminate of a variety of functional layers as described above. Examples of typical functional layers include an adhesive layer for closely attaching the laminate to the sealing material, a white layer for increasing the expression efficiency of the solar cell elements by supplying a reflection function of solar light which has transmitted through the transparent front substrate and the cell-side substrate, a weather-resistant layer preferably installed on the outermost layer of the protective sheet for a solar cell, and the like.
Although there are a variety of functions that the protective sheet for a solar cell is required to have as described above, among the functions, there is a particular demand for durability in a hot and humid environment which has a direct influence on the service life of the solar cell module. Particularly, from the viewpoint of the durability of the solar cell module in a hot and humid environment, it is most important to prevent the peeling of the sealing material from the protective sheet for a solar cell and the intrusion of moisture into the cell-side substrate. That is, there is a demand for a protective sheet for a solar cell having a favorable adhesion to a sealing material used in a solar cell module in a hot and humid environment.
However, for the outmost layer of the back sheet for a solar cell which is in contact with the sealing material used in the solar cell module, the adhesion in an ordinary environment let alone the adhesion in a hot and humid environment have been rarely studied. For example, Patent Literature 1 simply describes that a back sheet for a solar cell is stacked on a filler (sealing material) made of an ethylene-vinyl acetate copolymer (hereinafter also referred to as EVA) and does not describe how the back sheet is attached to the filler. In addition, Patent Literature 1 describes a variety of aspects of a layer regarding the outermost layer of the back sheet for a solar cell on the sealing material side, but does not describe the adhesion to the sealing material. In addition, in Patent Literature 2, a back sheet for a solar cell and a sealing material used in a solar cell module are stacked through an extrusion resin layer made of a resin composition and are hot-pressed, but there is no description of the composition or properties of the extrusion resin layer.
Meanwhile, an example in which an adhesive layer is provided between a sealing material used in a solar cell module and the outermost layer of a back sheet for a solar cell on a sealing material side is described. For example, Patent Literature 3 describes a back sheet for a solar cell in which a deposited film of an inorganic oxide is provided on a single surface of a base material film, and heat-resistant polypropylene-based resin films including a whitening agent and an ultraviolet absorbent are stacked on both surfaces of the base material film provided with the deposited film of the inorganic oxide, and Patent Literature 3 discloses an aspect in which a sealing material made of EVA is stacked on the outermost layer of the back sheet for a solar cell using an acrylic adhesive layer in examples.
Meanwhile, in recent years, an example in which the material of the outermost layer of the back sheet for a solar cell on the sealing material side is studied and the direct adhesion between the sealing material used in the solar cell module and the outermost layer of the back sheet for a solar cell on the sealing material side is studied has been also known to a slight extent (refer to Patent Literature 4). Patent Literature 4 describes an aspect in which the back sheet for a solar cell configured of at least two or more layers including a weather-resistant base material film has an adhesive coated layer colored with a white pigment mainly including titanium oxide on an innermost surface that is adhered to a filler configuring a solar cell module of the solar cell back sheet. Patent Literature 4 describes that an acrylic resin, an epoxy-based resin, a phenol-based resin, a polyester-based resin, an urethane-based resin, a styrene-based resin, a silicon-based resin or a modifier thereof is preferably used as a resin for the adhesive coated layer having adhesion to EVA, and the resin preferably includes a polyacrylic resin among the above. In addition, Patent Literature 4 only discloses an aspect in which an adhesive coated layer including an acrylic resin and an acrylic acid resin into which a polyester skeleton has been introduced in examples.
Patent Literature 5 discloses a sheet obtained by coating a coating liquid including an olefin-based resin, an oxazoline compound and silicon, tin, zirconium and aluminum as fine particles on a PET film.
Patent Literature 6 discloses a sheet obtained by coating a coating liquid including an acid-modified polyolefin resin and an oxazoline crosslinking agent on a PET film.